Method and apparatus for film weave correction

Abstract

A method and apparatus for film weave correction is disclosed in connection with a moving beam-type recorder or flying spot scanner device having a continuous-motion film drive in which the film is edge-guided rather than sprocket hole-guided as during playback. The film weave correction apparatus causes the beam to sweep, at least once for each frame being scanned, horizontally across a sprocket hole defined in the film adjacent to the frame. A detector behind the film detects the beams's crossing of the sprocket hole edge. The apparatus compares the time of occurrence of this edge crossing with a reference time and generates therefrom a film weave correction signal. This signal is applied to the horizontal deflection circuitry of the device and causes the beam to be shifted in such a way that the horizontal position of each scanned frame remains constant with respect to the position of the adjacent sprocket hole rather than with respect to the film edge or film guide.

I claim: 
     
       1. The method of correcting film weave in a motion picture film recording or reproducing apparatus using a scanning device which employs a continuous motion film drive during scanning of the film over a plurality of frames of data comprising the steps of: (a) causing the scanning beam to horizontally cross the edge of a sprocket hole on said film;   (b) detecting said beam as it crosses said sprocket hole edge and generating an edge crossing occurrence signal representative thereof;   (c) comparing this edge crossing occurrence signal with a reference time;   (d) generating a correction signal in response to the difference in time found in step (c) between said edge crossing time and said reference time;   (e) coupling said correction signal to a horizontal sweep circuit such that all beam sweeps in a given frame are shifted in horizontal position as a function thereof; and   (f) repeating of steps (a)-(e) for each frame scanned by said scanning device.   
     
     
       2. The method of correcting film weave in a motion picture film recording or reproducing apparatus using a scanning device which employs a continuous motion film drive during scanning of the film over a plurality of frames of data comprising the steps of: (a) causing the scanning beam to horizontally cross the edge of a sprocket hole on said film during each of a plurality of beam horizontal sweeps;   (b) detecting said beam as it crosses said sprocket hole edge during each sweep and generating edge crossing occurrence signals representative thereof;   (c) comparing each said edge crossing occurrence signal with a reference time;   (d) averaging the time differences found in step (c);   (e) generating a correction signal in response to said averaging of step (d);   (f) coupling said correction signal to a horizontal sweep circuit such that all beam sweeps in a given frame are shifted in horizontal position as a function thereof; and   (g) repeating of steps (a)-(f) for each frame scanned by said scanning device.   
     
     
       3. The method of correcting film weave in a film scanning device employing a continuous motion film drive during scanning of the film over a plurality of frames of data comprising the steps of: (a) shifting the sweep position of a plurality of horizontal sweeps of said beam, such that the beam crosses the edge of a sprocket hole on said film during each said sweep and such that beam position during such sweeps is independent of prior film weave correction signals;   (b) detecting said beam as it crosses said sprocket hole edge during each sweep and generating edge crossing occurrence signals representative thereof;   (c) generating a reference time pulse that is set to occur after the beam has crossed the edge of the sprocket hole during any said shifted sweep such that there is a positive time occurrence difference between each said edge crossing occurrence signal and the corresponding reference time pulse;   (d) gating each said edge crossing occurrence signal with said reference time pulse such that an output pulse is generated whose pulse width is equal to the time difference found between each said edge crossing occurrence signal and said reference time pulse;   (e) integrating the plurality of said output pulses such that an output level is generated whose amplitude is a function of the average of the pulse widths of said output pulses;   (f) updating a sample and hold means as a function of said output level;   (g) coupling the output of said sample and hold means as a film weave correction signal to a horizontal sweep circuit such that all beam sweeps in a given frame are shifted in horizontal position as a function thereof; and   (h) repeating of steps (a) through (g) for each frame scanned by said scanning device.   
     
     
       4. The method of claim 3 wherein step (b) includes the steps of: (i) detecting said beam as it crosses said sprocket hole edge and generating a beam signal in response thereto;   (ii) amplifying and base-line adjusting said detected beam signal;   (iii) squaring said amplified beam signal;   (iv) generating a window pulse during the time that a beam edge crossing is to occur; and   (v) gating said squared and amplified beam signal with said window pulse to generate thereby an edge crossing occurrence signal representative of said beam edge crossing.   
     
     
       5. The method of claim 3 wherein step (d) includes the steps of: (i) changing the state of a flip-flop as a function of the leading edge of each said edge crossing occurrence signal; and   (ii) resetting said flip-flop with said reference time pulse after each said state change such that said flip-flop is caused to return to its original state, said flip-flop being caused thereby to output an output pulse for each edge crossing occurrence signal, whose pulse width is equal to the time during which said flip-flop was in its changed state.   
     
     
       6. The method of claim 3 wherein step (e) includes the steps of: (i) inputting the plurality of said output pulses to an integrator;   (ii) inputting an offset signal to said integrator such that said offset signal normally keeps the level of integration of said output pulses within the operating range of said integrator; and   (iii) outputting an output level from said integrator whose amplitude is the integrated average of the pulse widths of said output pulses less the integrated value generated from said offset signal.   
     
     
       7. The method of claim 3 additionally comprising the steps of: (j) integrating the output of said sample and hold means such that a supplemental centering signal is generated thereby; and   (k) coupling said centering signal to said horizontal sweep circuit, said centering signal being additionally combined with the output of said sample and hold means when beam sprocket hole edge sweeps are not being performed.   
     
     
       8. In a motion picture film recording or reproducing apparatus having a scanning beam and beam horizontal deflection means for scanning a film as said film is moved past a scanning area by means of a continuous motion film drive, a film weave correction circuit for varying the horizontal sweep position of said beam as a function of detected film position error comprising: (a) means for enabling said beam to horizontally cross the edge of a sprocket hole defined on the film during at least one horizontal sweep of said beam, said means including means for disabling any prior generated film weave correction signal during such horizontal sweeps;   (b) detector means operatively positioned to detect said beam as the beam crosses the edge of said film sprocket hole and to output a beam edge crossing occurrence signal in response thereto;   (c) comparator means responsive to said beam edge crossing occurrence signal for comparing the time of occurrence of said detected beam edge crossing with a reference time; and   (d) means responsive to said comparator means for generating a film weave correction signal, said signal being coupled to said horizontal deflection means.   
     
     
       9. The apparatus of claim 8 wherein said detector means comprises: a beam detector operatively positioned such that said film is between said detector and said beam, and biased such that a beam signal is generated by said detector when said beam is incident thereon and not blocked by said film;   preamplifier means for amplifying said beam signal;   means for base line zeroing of said preamplifier means immediately prior to the expected occurrence of said beam edge crossing;   squaring means for generating a squared output signal as a function of said preamplified beam signal;   a window flip-flop operatively connected to turn on immediately prior to the expected occurrence of said beam edge crossing and operatively connected to turn off upon detection of a reference time pulse; and   gating means enabled by the turned on state of said window flip-flop to allow said squared output signal to be coupled as a beam edge crossing occurrence signal to said comparator means.   
     
     
       10. The apparatus of claim 9 wherein said beam detector comprises an antenna and said scanning beam is an electron beam. 
     
     
       11. The apparatus of claim 8 wherein said comparator means comprises: a pulse width flip-flop operatively connected to change state upon detecting said beam edge crossing occurrence signal, and operatively connected to reset upon detection of a reference time pulse, said flip-flop generating an output pulse whose pulse width is indicative of said sprocket hole edge position;   an integrator for integrating the time duration of said output pulse from said pulse width flip-flop, such that an output level is generated therefrom;   offset signal means operatively connected to said integrator such that as said integrator positively integrates the output of said pulse width flip-flop, said offset signal means continuously subtracts from said integration value generated by said integrator, such that the output level of said integrator remains within the operational limits of said integrator.   
     
     
       12. The apparatus of claim 11 wherein said means responsive to said comparator means for generating a film weave correction signal comprises: a sample and hold means operatively enabled to be updated by said integrator output level when said integrator has completed integration of said plurality of beam signals; and   filter means for filtering the output of said sample and hold means; said filter means output comprising said weave correction signal.   
     
     
       13. In a film scanning apparatus having a scanning beam and beam horizontal deflection means for scanning a film as said film is moved past a scanning area by means of a continuous motion film drive, said film including a plurality of sprocket holes defined thereon, a film weave correction circuit for varying the horizontal sweep position of said beam as a function of detected film position error comprising: (a) means for enabling said beam to horizontally cross the edge of a sprocket hole adjacent to a frame currently being recorded, said means providing a plurality of such crossings per each sprocket hole;   (b) detector means operatively positioned to detect said beam as the beam crosses the edge of said sprocket hole during each said beam edge crossing, and to output a beam edge crossing occurrence signal in response to each said edge crossing;   (c) means for generating a reference time pulse a specific time during each said horizontal sweep by said beam of said sprocket hole;   (d) a pulse width flip-flop operatively connected to change state and go on upon detecting each said beam edge crossing occurrence signal, and operatively connected to be reset and go off upon detection of said reference time pulse, said flip-flop generating output pulses thereby whose pulse widths are indicative of said sprocket hole edge position;   (e) an integrator for integrating the time duration of each of said plurality of output pulses from said pulse width flip-flop, generated from said plurality of beam horizontal edge crossings of said sprocket hole, such that an output level is generated therefrom which represents the average pulse width of said output pulses;   (f) offset signal means operatively connected to said integrator such that as said integrator positively integrates the output pulses from said pulse width flip-flop, said offset signal means continuously subtracts a fixed amount from said integration value generated by said integrator, such that the output level of said integrator remains within the operational limits of said integrator; and   (g) sample and hold means operatively enabled to be updated by said integrator output level when said integrator has completed integration of said plurality of beam edge crossing signals, said sample and hold means outputting a weave correction signal thereby, said signal being coupled to said horizontal deflection means.   
     
     
       14. The apparatus of claim 13 further comprising second integrator means operatively connected to continuously integrate the output of said sample and hold means and to generate a supplemental centering signal in response thereto; and means for coupling said centering signal to said horizontal deflection means, said means including means for additively combining said centering signal with the output of said sample and hold means when beam sprocket hole edge sweeps are not being performed.